Various kinds of semiconductor light emitting devices such as a lighting device having a semiconductor light emitting element (hereinafter, appropriately referred to as the “light emitting element”) have been developed, and means for improving an output performance have been variously studied. Especially, as for a light emitting device usable for a general lighting apparatus, it is important to have a high color rendering property (basically, a general color rendering index Ra is 80 or more in U.S. Energy Star standard, or the like) as its performance.
Representative methods for implementing a white light emission in the semiconductor light emitting device include firstly a method which uses three kinds of LED (light emitting diode) chips which emit red, green, and blue, secondly a method which combines a blue LED chip and a yellow or orange phosphor, thirdly a method which combines a blue LED chip, a green phosphor, and a red phosphor, and fourthly a method which combines an ultraviolet emission LED chip, a blue phosphor, a green phosphor, and a red phosphor. Among them, the second or third method is widely put into practical use in general.
In a structure of an LED device employing the above method, the LED chip is mounted on a cup part (concave part) of a wiring substrate, and a transparent sealing resin mixed with a phosphor is poured into the cup part and hardened to form a resin layer containing the phosphor (see patent document 1 and patent document 2, for example).
According to a light emitting device disclosed in the patent document 1, it has a structure in which a blue LED chip is used as a light emitting element, and three kinds of phosphors such as two kinds of yellow phosphors having different peak emission wavelengths and a red phosphor are mixed and dispersed in a transparent resin to form a phosphor layer. Especially, the two kinds of the yellow phosphors include a first yellow phosphor having a peak emission wavelength of 540±20 nm, and a second yellow phosphor having a peak emission wavelength longer than the peak emission wavelength of the first yellow phosphor but 590 nm or less, and by adjusting a mixture ratio of the red phosphor, light emission luminance is prevented from being reduced as much as possible, and a relatively high color rendering property and high light emission luminance are achieved at the same time.
According to a light emitting device disclosed in the patent document 2, a peak emission wavelength is elongated by adding Al and B in a nitride phosphor serving as a red phosphor, so that a deeper red light emission is provided, and a phosphor layer is configured in combination with another phosphor (such as green phosphor, or yellow phosphor), so that a white light emission is provided.